1. Field of the Invention
The present invention relates generally to connectors, and more particularly to a connector for passively aligning a light source or detector to an optical waveguide such as a fiber optic cable or bundle.
2. Description of the Prior Art
Communication systems are now being developed in which optical waveguides such as optical fibers are used as conductors for modulated light waves to transmit information. These fibers may be utilized for long distance communication networks, fiber to the home networks, wide area networks, or local area networks.
The communication networks used comprise at least a connector between the optical waveguide and a detector or light emitter. These detectors convert the signal from the light waves to an electrical signal which may be used by conventional electrical devices such as a computer. The light emitters, on the other hand, perform the opposite function. They convert an electrical signal into an optical signal. A generic term of either a light emitter or a detector is an "optoelectronic transducer."
This application addresses the efficiency of optical coupling between an optical waveguide and an optoelectronic transducer. High efficiency coupling requires: 1) close matching of the sizes of the light beam and the waveguide; 2) close matching of the angular extent of the light beam with the acceptance angle of the waveguide; and 3) close positional alignment between the light beam and the waveguide. Furthermore, real world effects such as temperature changes, may change the alignment. For this reason, many commercial couplers compromise efficiency for slight positional tolerances. For example, the light beam may be focused to a spot smaller than the waveguide with the inevitable result that some light will be lost in the waveguide.
The prior art has also addressed the alignment problem by actively aligning the above elements. The major disadvantage of active alignment is the cost associated with this process. For example, for a device to be actively aligned, the light source needs to be turned on and the other elements aligned with the light source while the device is activated. By using this approach, one must carefully align each device produced. Obviously, this is not preferably if one is to mass produce these elements.
There are numerous patents which teach active alignment as discussed above. For example, U.S. Pat. No. 4,204,743, by Etaix, discloses an actively aligned connector for coupling an optical fiber to a light emitter or receiver. This reference teaches the use of a truncated cone in order to facilitate its contacting the emitter or receiver without being obstructed by electrical connections to the emitter or receiver. This device is activated to align the emitter with the optics. Additionally, this device is very intolerant to off axis alignment of the optical lenses.
U.S. Pat. No. 4,307,934, by Palmer, discloses a packaged fiber optic module which utilizes two oppositely oriented convex lenses to transmit light between a light source and a fiber bundle. Because of the use of this particular construction, the distance between the fiber bundle and its associated convex lens is critical since this lens functions to focus the light beam generated by the light source. Therefore, it is essential that active alignment be utilized in this device. Additionally, this device is very intolerant to off axis alignment of the optical lenses.
U.S. Pat. No. 4,687,285, by Hily et al, discloses a packaged fiber optic module which utilizes two oppositely oriented plano-convex lenses in combination with a ball lens to transmit light between a light source and a fiber bundle. As may be seen, the axis of each lens must be in perfect alignment for this system to function properly. Therefore, this device is very intolerant to off axis alignment of the optical lenses. This reference also teaches the use of an adhesive to allow the ball lens to be manipulated during the active alignment process.
U.S. Pat. No. 4,687,285, by Haberland et al, discloses a packaged fiber optic module which has an active alignment positioning means. In addition, this reference teaches the use of a single spherical or cylindrical lens for focusing a light beam from a fiber optic cable onto a detector. As may be seen in FIG. 8, it is critical to align this spherical lens to the cable in order to achieve coupling between the cable and the detector. Therefore, this device is very intolerant to off axis alignment of the optical lenses.
U.S. Pat. No. 4,711,521, by Thilays, discloses a terminal device for an optical fiber. A mechanical guiding operation, by means of a pin, is used to actively position a ball lens with respect to a fiber optic cable end. The ball lens utilized by this reference must be the same order of magnitude as the exit aperture, e.g., 80 to 100 microns for the ball lens and 200 microns for the aperture. This is an essential to allow precision alignment. Therefore, this device is very intolerant to off axis alignment of the optical lens with the aperture.
U.S. Pat. No. 4,753,508, by Meuleman, discloses an optical coupling device which utilizes a reflective cavity to provide optical coupling between a fiber cable and a light emitter. A spherical lens is aligned with the optical axis of the fiber cable and is disposed outside of the reflective cavity. Precision active alignment of the spherical lens to the fiber cable is essential for the operation of this device. Therefore, this device is very intolerant to off axis alignment of the optical lens.
U.S. Pat. No. 5,347,605, by Isaksson, discloses an optoelectronic connector which is actively aligned. To perform this alignment, a mirror is provided which is journaled and is adjusted to provide maximum coupling efficiency while the light source is active.
U.S. Pat. Nos. 5,537,504, and 5,504,828, both by Cina et al., disclose a transducer, a spherical lens and an optical fiber cable in axial alignment with one another. This is accomplished by activating the transducer and aligning the spherical lens with respect to the fiber cable. Once this is done, the position of the laser and lens is fixed by heating an epoxy layer. In addition, the spherical lens is provided with different surfaces, one for collimating light and one for introducing a spherical aberration that compensates for lens position. Precision active alignment of the spherical lens to the fiber cable is essential for the operation of this device. Therefore, this device is very intolerant to off axis alignment of the optical lens, even with the second surface of the spherical lens.
U.S. Pat. No. 4,842,391, by Kim et al., discloses an optical coupler which utilizes two spherical lenses between a laser diode and a fiber cable. As may be seen, active alignment is provided by a set of screws which is used to actively align the optical elements to increase coupling efficiency.
U.S. Pat. Nos. 4,265,511 and 4,451,115, both issued to Nicia et al. disclose the use of two ball lenses for coupling optical fibers. In a similar fashion, U.S. Pat. No. 5,175,783, by Tatoh, discloses a similar structure. These patents disclose the concept of carefully aligning each fiber in a tube to a precise axial and distance position with respect to its respective ball lens. Therefore, these devices are very intolerant to off axis alignment of the optical lens.
Other patents which disclose active alignment of a lens to a fiber cable include: U.S. Pat. No. 5,526,455, by Akita et al.; U.S. Pat. No. Re 34,790, by Musk; U.S. Pat. No. 5,073,047, by Suzuki et al; U.S. Pat. No. 4,824,202, by Auras; U.S. Pat. No. 4,818,053, by Gordon et al; U.S. Pat. No. 4,790,618, by Abe; U.S. Pat. No. 5,452,389, by Tonai et al.; and U.S. Pat. No. 4,752,109, by Gordon et al. Precision active alignment of the lens to the fiber cable is essential for the operation of these devices. Therefore, these devices are very intolerant to off axis alignment of the optical lens to the light source.
The prior art has addressed this issue of off axis alignment of the fiber cable and the light source. For example, U.S. Pat. No. 5,566,265, by Spaeth et al., discloses a module for bi-directional optical signal transmission. In this device, a plano-convex lens is aligned with the optical axis of a fiber cable and a beam splitter is aligned with a edge emitting light source. By adjusting the beam splitter in relation to the plano-convex lens, one may correct for off axis alignment of the light source and the fiber cable. In a similar fashion, U.S. Pat. No. 5,463,707, by Nakata et al., discloses the use of a barrel lens instead of a plano-convex lens. U.S. Pat. No. 5,546,212, by Kunikane et al., discloses the use of a prism instead of a beam splitter. U.S. Pat. No. 5,074,682, by Uno et al., discloses the use of a Grin rod lens instead of a beam splitter.
The prior art has also addressed methods for aligning a spherical lens with a light source. For example, U.S. Pat. No. 4,740,259 by Heinen, and U.S. Pat. No. 4,501,637, by Mitchell et al., both discuss aligning a spherical lens to a Light Emitting Diode (LED). Neither of these references address the problems associated with utilizing these structures in a coupling device.